Nanofabricated structures for sub-beam resolution and spectral enhancement in tomographic imaging

ABSTRACT

Techniques are provided for tomographic imaging with sub-beam resolution and spectral enhancement. A system implementing the techniques according to an embodiment includes a target structure comprising one or more selected materials nanopatterned on a first surface of the target structure in a selected arrangement. The system also includes a primary particle beam source to provide a particle beam incident on an area of the first surface of the target structure, the area encompassing one or more of the nanopatterned materials, such that the materials generate characteristic X-rays in response to the primary beam. The system further includes a spectral energy detector (SED) to perform individual photon counting and spectral analysis of the characteristic X-rays and estimate attenuation properties of the imaged sample. The sample is positioned both adjacent to a second surface of the target structure, opposite the first surface, and between the target structure and the SED.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/923,756, filed Oct. 21, 2019, which is incorporatedby reference herein in its entirety.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with United States Government assistance underContract No. FA8650-17-C-9114, awarded by the United States Air Force.The United States Government has certain rights in this invention.

FIELD OF DISCLOSURE

The present disclosure relates to X-ray imaging, and more particularly,to a system using nanofabricated structures to provide sub-beamresolution and spectral enhancement in tomographic imaging.

BACKGROUND

There exists a need for non-destructive, 3-dimensional (3D) imaging ofobjects of interest at ever-increasing resolutions. For example,integrated circuits (ICs) are being fabricated with nanometerdimensional features such as in the range of 14 nanometers (nm), 7 nm,and smaller. High-resolution imaging of these circuit features isimportant for testing, verification, and research purposes, to name afew. Yet, many existing imaging techniques such as table-top X-raysystems, optical microscopy, and infrared imaging are limited tomicron-level resolution and spectrally narrow imaging, which isinsufficient for many applications. Existing high-resolution imagingtechniques such as scanning electron microscopy (SEM), transmissionelectron microscopy (TEM) and atomic force microscopy (AFM) suffer fromlow-throughput and provide only 2D images, although 3D images arepossible via sample destruction (e.g., delayering). Various modalitiesavailable at synchrotron end-stations can provide tomographic imaging atthe nanometer scale, however this is a resource of limited availabilityand high expense.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 illustrates an imaging system employing a nanofabricated targetstructure, configured in accordance with certain embodiments of thepresent disclosure.

FIG. 2 illustrates a planar view of the nanofabricated target structure,configured in accordance with certain embodiments of the presentdisclosure.

FIG. 3 is a more detailed illustration of the imaging system employing ananofabricated target structure, configured in accordance with certainembodiments of the present disclosure.

FIG. 4 illustrates dimensions and arrangement of the nanostructuresdisposed on the fabricated target structure, in accordance with certainembodiments of the present disclosure.

FIG. 5 illustrates the use of spacers and stacked nanomaterials, inaccordance with certain embodiments of the present disclosure.

FIG. 6 illustrates image processing results from an imaging systememploying a nanofabricated target structure, configured in accordancewith certain embodiments of the present disclosure.

FIG. 7 is a flowchart illustrating a methodology for imaging using thenanofabricated target structure, in accordance with another embodimentof the present disclosure.

FIG. 8 is a block diagram schematically illustrating a platformemploying the disclosed imaging techniques, in accordance with certainembodiments of the present disclosure.

Although the following Detailed Description will proceed with referencebeing made to illustrative embodiments, many alternatives,modifications, and variations thereof will be apparent to those skilledin the art.

DETAILED DESCRIPTION

Techniques are provided for achieving sub-beam imaging resolution andspectral enhancement of tomographic imaging through the use ofmulti-material nanofabricated target structures which emit secondaryX-rays in response to illumination from a primary particle beam source.The term “sub-beam” resolution refers to the fact that resolutiondimensions may be achieved, by the secondary X-rays, which are smallerthan the diameter of the primary particle beam, as will be explained ingreater detail below.

Overview

As noted previously, there exists a need for non-destructive,3-dimensional (3D) imaging of objects of interest at ever-increasingresolutions, for example, in the range of 14 nm, 7 nm, and smaller.Imaging of physical features can provide feedback for processimprovement, increasing reliability and yield while reducing costs.Manufacturing variability is a particular concern in nanoscalefabrication since high variance in physical features can changeperformance characteristics, predispose a device to early failure, orproduce undesired or unexpected outcomes such as short-circuits andlarge changes in threshold voltage, for example. At the nanoscale, thevariance can approach the mean size of the features. Non-destructive 3Dimaging can also be used to inspect microelectromechanical systems(MEMS), welding joints, additively-manufactured parts, grain structureand defects in materials, in-situ material growth under variableconditions, and structural evolution of in-operando nano-scaled devices.

X-rays have high energies and indices of refraction nearly equal to 1,making them suitable for high resolution (sub-micrometer) projection andtomographic imaging. Unfortunately, photons at these energies areparticularly difficult to focus and require a relatively large space forfocusing optics. Synchrotron beamline end-stations can provide this highresolution capability, but as stated previously, access to suchfacilities is limited. Benchtop systems may not provide the room neededfor complex optical arrangements, and they generally do not providespectrally wide X-ray sources that can be used to analyze all of thematerials in a chemically diverse sample simultaneously.

To this end, and according to an embodiment of the present disclosure, ananofabricated target structure is positioned between a primary particlebeam source and a sample specimen to be imaged. Selected materials aredisposed on one surface of the target structure (or substrate) whichfaces the primary beam source. These materials are referred to asnanostructures since they generally have sub-micron diameters, and theprocess of disposing these materials on the target structure is referredto as nanofabricating or nanopatterning.

Due to various interactions with particles (electrons, X-rays or lowatomic number ions) in the primary beam, the nanostructures emitsecondary X-ray radiation consisting of (i) characteristic X-rays withknown energies unique to the element composition of the nanostructuresand the incident energy of the primary particles, and (ii) other typesof X-rays such as Bremsstrahlung for the case of incident electrons. Ingeneral, the primary particles interact not only with thenanostructures, but also with the target substrate and potentially withthe imaged sample. In the case of incident electrons, there may bemultiple scattering events in the forward and backward directions; afterhaving propagated through the nanostructure, an electron may backscatterinto the material again and generate another X-ray. In the case ofincident photons, an additional fluorescence event may occur, in which aphoton generates a new photon either in the nanostructure or externallyto the nanostructure. That X-ray may subsequently undergo additionalphoton-generating processes within the nanomaterial.

Regardless of the photon-generating history, however, characteristicX-rays with a priori known energies are generated in the nanostructurevolume, and, provided that each lateral dimension of the volume issmaller than the primary beam diameter, so-called sub-beam resolutionmay be achieved. These X-rays can be used to improve resolution intomographic imaging, if the measurement system is energy-sensitive suchthat detected characteristic X-rays may be associated with a “focalspot” corresponding to a nanostructure volume. Continuum X-rays such asBremsstrahlung, and any scattering event that does not correspond tocharacteristic fluorescence from target materials, cannot be used toachieve sub-beam resolution, as these X-rays can originate from anypoint within the target/sample assembly. An energy sensitive detectormay be used to discriminate these X-rays from characteristic X-raysarising from within the nanostructures.

Characteristic X-rays generated from the target nanostructures propagatethrough the sample to be imaged, and the energy sensitive detector canbe used to either perform individual photon counting or acquireintensity measurements as a function of photon energy. In someembodiments, given an initial source model, a description of the photoninteraction physics with the sample, and a suitable inversion ortomographic formalism, the properties of the sample can be deduced athigh resolution from the measurements, as will be described in greaterdetail below.

The increased imaging resolution provided by embodiments of the presentdisclosure can be employed at incident particle energy levels andparticle flux levels that are non-destructive to the nanostructures andsample. Particularly for the case of “benchtop sources” or “weaksources,” a detector displaying high signal-to-noise ratio capability,or a statistical tomographic processing system well-suited to low signallevels, has the potential to accommodate low incident particle flux.

The disclosed techniques can be used in a wide variety of applicationsincluding, for example, quantifying IC feature variability for qualitycontrol, identifying IC counterfeiting to deter intellectual propertytheft, detecting presence of malware introduced into ICs manufactured bythird parties, and IC failure analysis. Other applications includeinspection of microelectromechanical systems (MEMS), welding joints,additively-manufactured parts, grain structure and defects in materials,in-situ material growth under variable conditions, and structuralevolution of in-operando nano-scaled devices.

In accordance with an embodiment, a methodology to implement thesetechniques includes providing a primary particle beam to illuminatematerials nanopatterned on a first surface of a target structure,hereinafter referred to as a target structure or just target. The targetstructure may also be referred to as a planar structure since the widthand height dimensions of the target surfaces are typically much greaterthan the thickness of the target. The first surface of the target is amaterial distinct from the selected disposed materials. The illuminatedvolume encompasses two or more selected materials nanofabricated on afirst surface of the target structure, such that the two or moreselected materials generate X-ray photons in response to the primaryparticle (photon, electron or low atomic number ion) beam.

The methodology further includes detecting, for example using a spectralenergy detector (SED) or energy-dispersive X-ray (EDX) detector,individual photons or intensity levels implicitly containing X-rayinformation on the sample specimen to be imaged due to sampleinteractions. In one embodiment, the data is processed to inferattenuation contrast in the sample at the given energy of thecharacteristic X-rays. Multiple attenuation contrast images may begenerated, each corresponding to the given characteristic X-rays. In oneembodiment, X-ray photon counts from different energies (differentcharacteristic X-rays) are inverted jointly for an element densitymodel.

The sample is positioned both adjacent to the second surface (oppositethe first surface) of the planar target structure, and between theplanar target structure and the SED. In some embodiments, a spacer maybe positioned between the target structure and the sample, the spacerfabricated from a material with a low attenuation composition (e.g.,aluminum). In another embodiment, there may be an air-gap between thetarget structure and the sample. The focal spot size of thecharacteristic fluorescent X-rays in the nanostructures aresubstantially related to the area and depth of the selected materialsthat generate these photons, and the area is generally smaller than thefootprint of the primary particle beam.

It will be appreciated that the techniques described herein may provideimproved imaging resolution, compared to other possible techniques, suchas those that use imaging beams with relatively large diameterbeamwidths or imaging beams generated at power levels that can destroythe sample being imaged. Other applications will be apparent.

System Architecture

FIG. 1 provides a top-level illustration of an imaging system 100employing a nanofabricated target structure, configured in accordancewith certain embodiments of the present disclosure. The imaging systemis configured to provide sub-beam imaging resolution and spectralenhancement through the use of multi-material nanofabricated targetstructures. As shown, a primary imaging beam source 160 is configured togenerate a primary imaging beam that illuminates the target structure130. In some embodiments, the primary beam may be an X-ray beam, anelectron beam, or a low atomic number ion beam. The sample to be imaged140 is positioned behind the target 130, for example on a fixture 120.As will be described in greater detail below, nanostructures disposed onthe surface of the target 130 generate characteristic X-rays in responseto the primary beam. These secondary X-rays emanate from a lateral areasmaller than the primary beam footprint, thus imaging resolution islimited by the size of the nanostructures rather than the size of theincident primary beam spot. The secondary X-rays pass through the sample140 and are detected by spectral energy detector 150. The measuredphoton count at a given characteristic X-ray energy may then be used toconstruct an image of the sample 140. In some embodiments, multiple datasets may be obtained, for example as the sample and the target undergorotation and/or translation, and these multiple data sets may betomographically processed 110 to provide a detailed three-dimensionalview of the sample 140.

In one embodiment, no rotations are performed, and instead a projectionimage is obtained using a single nanomaterial “point source” in which animage is formed on a detector pixel array. In another embodiment, norotations are performed, and instead a projection image is obtainedusing a single nanomaterial “point source” in which a single detectorpixel is translated to a new location to collect another measurement;after the conclusion of a suitable raster scan in two-dimensions usingsuch translations, a projection image may be constructed. Thiscorresponds to “synthetic aperture” as opposed to “real aperture,” andthe projection image (for a single characteristic energy) reveals, inessence, an attenuation measurement of the sample.

FIG. 2 illustrates a planar view of the nanofabricated target structure130, configured in accordance with certain embodiments of the presentdisclosure. The surface of the target structure 130 facing the primarybeam source 160 is shown. Nanostructures 200 are fabricated on thesurface in a selected pattern as illustrated. The nanostructures may becylindrical or cuboids, though other volumetric shapes are possible. Insome embodiments, the nanostructures may be composed of any one or moreof various materials such as hafnium (Hf), tantalum (Ta), tungsten (W),bismuth (Bi), gold (Au), lead (Pb), zinc (Zn), copper (Cu), germanium(Ge), titanium (Ti), chromium (Cr), nickel (Ni), and platinum (Pt). Thematerials are selected to accommodate the primary beam energy as well asthe gamut of absorption edges in the sample. The source beamwidth 210(footprint or profile) is illustrated by the circular dotted line and isshown to encompass several (e.g., 9) of the nanopatterned materials 200,in each of three instances of target illumination. An alternatehexagonal pattern/arrangement 220 of the materials is also shown, as maybe used in some embodiments. This pattern may advantageously allow theprimary source beam width to fully cover a pre-selected number (e.g., 7)of nanostructures without partially impinging on neighboring materials.This allows for correctly associating a detector measurement with thelocation of the nanostructures that gave rise to that data. In thisillustration, the nanopatterned materials are shown to be circular witha diameter of 300 nanometers.

The nanostructures can be patterned directly onto an X-ray-transparentsubstrate or thin (<200 nm) membrane of, for example, diamond or siliconnitride. Optionally, as a means of promoting charge and thermaldissipation, the nanostructures can be fabricated on thin films of metalsuch as gold or aluminum that have been deposited on top of thesemembranes. For additional structural support and increased charge andthermal dissipation in the case of a high-powered beam, the structurescan be embedded inside of an X-ray transparent substrate such asgraphite or diamond such that the targets are completely surrounded. Insome such embodiments, voids may be created inside of the substrate,into which the target materials can be deposited.

FIG. 3 is a more detailed illustration 300 of the imaging systememploying a nanofabricated target structure, configured in accordancewith certain embodiments of the present disclosure. The primary beamsource 160 is shown to generate the primary beam 320, which illuminatesseveral of the nanopatterned materials of target 130, as shown in across-sectional side view. Each of the nanopatterned materials generatesX-rays 310 that emit isotropically in response to the primary beam 320.Beam 320 may be a focused beam of electrons originating from a benchtopelectron column (i.e., SEM), or a focused beam of photons generated, forexample at a synchrotron, and filtered and focused using X-ray optics.The beam may also comprise low atomic number ions (i.e., protons),although damage to the nanostructures over time is more likely withthese particles. Each of the X-ray photon 310 energies and flux levelsare determined by the composition of the nanostructures, by the primarybeam 320 particle type, and by the energy of those incident particles.Nanostructure volume also determines photon flux levels.

The characteristic X-rays 310 pass through the sample 140 and areaffected (e.g., attenuated) to varying degrees by the internal structure340 of the sample. Sensors 330 of spectral energy detector 150 areconfigured to detect these X-rays after passage through the sample 140.The detected photons may be spatially attributed to known sourcelocations by virtue of the correspondence between their measuredenergies and the known characteristic spectral lines produced by eachtarget material. An image may thus be formed based on the signalsgenerated by each sensor. Stated differently, each sensor may beconsidered to represent a pixel of a composite image representing theinternal structure of the sample 140.

In some embodiments, rather than creating a 2D projection image, themeasured data may be tomographically processed for construction of a 3Dimage of the sample, particularly if the data collection protocolprovides data with the necessary sensitivity to the 3D sample structure.Typically, this involves translating the target/sample assembly withrespect to the beam for “dwell periods” and data collections at variouslocations, and doing so for various rotation angles of the assembly.Alternatively, a large flat panel array of detector pixels, or ahemispherical distribution of detector pixels may be used to eitherreduce or eliminate the need for multiple target/sample rotations anddata collections.

In some embodiments, the sensors 330 may provide high spectralresolution for distinguishing the energies of the fluorescent X-raysemitted by the various nanomaterials. In essence, a 2D pixel arraycoverage yields a 3D data set, the third dimension being energy.Additionally, measurement of detected X-rays may be used to identify thechemical composition of structures in the sample by joint inversion ofthat data for constituent element density in the sample, as thedifferential attenuations of each characteristic X-ray line variesaccording to the materials it interrogates. Taken together, they providea constraint on the possible material composition of the sample, ratherthan an attenuation contrast image at a single energy.

The sample 140 and target 130 are shown to be mounted on a fixture 120of any suitable type. In some embodiments, the fixture is configured toprovide rotational and/or translational motion to the sample and targetcombination. Multiple images of the sample may thus be obtained fromvarying viewpoints and these images may be processed tomographically toprovide a detailed three-dimensional estimation of the sample.Additionally, as numerous, distinct, characteristic X-ray energies aregenerated from the several target nanostructures simultaneously, andeach distinct X-ray energy interacts uniquely with the sample,complementary yet independent information is provided for volumereconstruction. This process may adopt numerous forms, and in oneembodiment is known as “spectral computed tomography.” In general, anysuitable tomographic inversion algorithm may be employed to reconstructa 3D image based on the measured X-ray interactions with the sample ascollected over a multiplicity of dwell locations and target/samplerotation angles.

In some embodiments, the SED 150 may be translated and/or rotatedinstead of (or in addition to) the fixture 120, as an alternativetechnique for obtaining varying viewing angles for tomographicprocessing.

FIG. 4 illustrates example dimensions and arrangement 400 ofnanostructures disposed on a target structure, in accordance withcertain embodiments of the present disclosure. In this example, threematerials (gold, platinum and tungsten) are patterned in groupings 420.The groupings are arranged in a hexagonal pattern 410 on the targetstructure. The spacing between groupings is chosen to accommodate thewidth of the primary beam such that neighboring groupings ofnanostructures are not simultaneously illuminated. The gold, platinumand tungsten structures have diameters of 250 nm, 750 nm and 500 nm,respectively. As photon flux levels vary as a function of the materialfor a given primary beam energy, diameters are chosen such that allthree materials achieve similar total photon counts over a chosen dwelltime.

FIG. 5 illustrates the use of spacers and stacked nanomaterials, inaccordance with certain embodiments of the present disclosure. Spacerlayers 500 are shown to be interposed between the nanopatternedmaterials 200 and the sample 140. Two spacer layers are shown. The firstspacer layer is a layer of gold approximately 100 nm thick. The secondspacer layer is a layer of aluminum approximately 1 micron thick. Insome embodiments, the spacer layers are employed to dissipate heat andto mitigate or prevent charge buildup on the sample (for example, as mayoccur with non-conducting sample materials). In some embodiments, thespacer layers are employed to introduce a magnification factor byallowing the isotropically emitted fluorescent X-rays in thenanostructures to spread out or widen before reaching the sample. Thisprovides an alternative approach to setting the imaging resolution (inaddition to controlling the area of the deposited nanomaterials). In oneembodiment, the first spacer layer may be viewed as a target layer. Thislayer in FIG. 5 is the 100 nm Au layer. Fluorescent emissions from thatlayer may also be used for tomographic processing.

In some embodiments, the nanopatterned materials may be configured in astacked arrangement, as shown at 510, such that the secondary X-raybeams 310 comprise a combination of energies emitted by the materials ineach stack. This technique can impart a highly spectrally diverse X-raysource depending on the materials selection as well as the particle typeand energy of the primary source beam. In such a case, the imagingmagnification factor for each collected image associated with adifferent material would be slightly different, as the distance betweenthe target material and imaging sample varies with position in thestack.

FIG. 6 illustrates image processing results from an imaging systememploying a nanofabricated target structure, configured in accordancewith certain embodiments of the present disclosure. The sample beingimaged 140, is shown to be an array of copper (Cu) structures 610, eachapproximately 1 micron by 1 micron laterally and 1 micron in height. Theprimary beam used in this example projects a 2 micron diameter spot, andis thus wider than the structural features of interest in the sample140.

The target nanostructures used in this example are gold (Au) cylinderswith 500 nm diameter and 1 micron height patterned on a 100 nm thicksilicon nitride membrane. A projected image of the Cu structuresresulting from Au characteristic X-ray attenuation through the sample isshown as a map 630, with axes in millimeters (mm). The variableattenuation of X-rays is represented here as detected photon count 620coded by the color scale on the right-hand side of the image.

As shown, the imaging system provides a magnification factor as thecharacteristic Au X-rays project outward from the sample 140 to thedetector 150. In this example, a magnification factor of 10,000 isachieved, wherein the imaged structures are approximately 10 mm wide,while the sample structures are approximately 1 micron wide.

Methodology

FIG. 7 is a flowchart illustrating a methodology for imaging using thenanofabricated target structure, in accordance with another embodimentof the present disclosure. As can be seen, example method 700 includes anumber of phases and sub-processes, the sequence of which may vary fromone embodiment to another. However, when considered in aggregate, thesephases and sub-processes form a process for imaging with sub-beamresolution and with multiple X-ray energies, in accordance with certainof the embodiments disclosed herein. These embodiments can beimplemented, for example using the system architecture illustrated inFIGS. 1-5, as described above. However other system architectures can beused in other embodiments, as will be apparent in light of thisdisclosure. To this end, the correlation of the various functions shownin FIG. 7 to the specific components illustrated in FIGS. 1-5 is notintended to imply any structural and/or use limitations. Rather otherembodiments may include, for example, varying degrees of integrationwherein multiple functionalities are effectively performed by onesystem. Numerous variations and alternative configurations will beapparent in light of this disclosure.

As illustrated in FIG. 7, in one embodiment method 700 commences, atoperation 710, by providing a primary particle beam (e.g., photon,electron, or ion beam) to illuminate nanostructures patterned on a firstsurface of the target structure. The primary particle beam causes one ormore selected materials to generate secondary (or characteristic) X-raysthat isotropically propagate from the nanostructures. These secondaryX-rays have characteristic energies that are based on properties of thenanostructure materials. The secondary X-rays originate from a spot witha width approximately equal in size to the selected nanostructures,which are chosen to be smaller than the primary beam width, thusenabling higher resolution imaging (when coupled with an appropriateenergy-sensitive X-ray detector).

Next, at operation 720, a spectral energy detector (SED) detects andmeasures the secondary X-rays which are attenuated by propagationthrough a sample to be imaged. The SED performs photon counting withinenergy bins of some given spectral resolution. When compared to theexpected source flux, a constraint on the attenuation structure of thesample is obtained. The sample is positioned both adjacent to the secondsurface of the planar target structure (opposite the first surface) andbetween the planar target structure and the SED.

Of course, in some embodiments, additional operations may be performed,as previously described in connection with the system. These additionaloperations may include, for example, rotating and/or translating thetarget structure and the sample, relative to the source of the primaryparticle beam, to provide tomographic imaging capability. In someembodiments, the selected materials may include, but are not limited to,for example, hafnium, tantalum, tungsten, bismuth, gold, lead, zinc,copper, germanium, titanium, chromium, nickel, or platinum. In someembodiments, the diameters of the select materials, as disposed on thetarget, are in the submicron range.

Example Platforms

FIG. 8 is a block diagram schematically illustrating a platform 800employing the disclosed imaging techniques, in accordance with certainembodiments of the present disclosure. In some embodiments, platform 810may be hosted on, or otherwise be incorporated into or any othersuitable platform or application.

In some embodiments, platform 810 may comprise any combination of aprocessor 820, a memory 830, an input/output (I/O) system 860, a userinterface 862, a display element 864, a storage system 870, a networkinterface 840, tomographic processing system 110, and fixture motioncontrol system 850. Platform 800 may be coupled to spectral energydetector 150 to receive detected signals for processing, for example bytomographic processing system 110. As can be further seen, a bus and/orinterconnect 890 is also provided to allow for communication between thevarious components listed above and/or other components not shown.Platform 800 can be coupled to a network 842 through network interface840 to allow for communications with other computing devices, platforms,devices to be controlled, or other resources. Other componentry andfunctionality not reflected in the block diagram of FIG. 8 will beapparent in light of this disclosure, and it will be appreciated thatother embodiments are not limited to any particular hardwareconfiguration.

Processor 820 can be any suitable processor, and may include one or morecoprocessors or controllers, such as an audio processor, a graphicsprocessing unit, or hardware accelerator, to assist in control andprocessing operations associated with platform 800. In some embodiments,the processor 820 may be implemented as any number of processor cores.The processor (or processor cores) may be any type of processor, suchas, for example, a micro-processor, an embedded processor, a digitalsignal processor (DSP), a graphics processor (GPU), a network processor,a field programmable gate array or other device configured to executecode. The processors may be multithreaded cores in that they may includemore than one hardware thread context (or “logical processor”) per core.Processor 820 may be implemented as a complex instruction set computer(CISC) or a reduced instruction set computer (RISC) processor.

Memory 830 can be implemented using any suitable type of digital storageincluding, for example, flash memory and/or random-access memory (RAM).In some embodiments, the memory 830 may include various layers of memoryhierarchy and/or memory caches as are known to those of skill in theart. Memory 830 may be implemented as a volatile memory device such as,but not limited to, a RAM, dynamic RAM (DRAM), or static RAM (SRAM)device. Storage system 870 may be implemented as a non-volatile storagedevice such as, but not limited to, one or more of a hard disk drive(HDD), a solid-state drive (SSD), a universal serial bus (USB) drive, anoptical disk drive, tape drive, an internal storage device, an attachedstorage device, flash memory, battery backed-up synchronous DRAM(SDRAM), and/or a network accessible storage device.

Processor 820 may be configured to execute an Operating System (OS) 880which may comprise any suitable operating system, such as Google Android(Google Inc., Mountain View, Calif.), Microsoft Windows (MicrosoftCorp., Redmond, Wash.), Apple OS X (Apple Inc., Cupertino, Calif.),Linux, or a real-time operating system (RTOS). As will be appreciated inlight of this disclosure, the techniques provided herein can beimplemented without regard to the particular operating system providedin conjunction with platform 800, and therefore may also be implementedusing any suitable existing or subsequently-developed platform.

Network interface circuit 840 can be any appropriate network chip orchipset which allows for wired and/or wireless connection between othercomponents of device platform 800 and/or network 842, thereby enablingplatform 800 to communicate with other local and/or remote computingsystems, servers, cloud-based servers, and/or other resources. Wiredcommunication may conform to existing (or yet to be developed)standards, such as, for example, Ethernet. Wireless communication mayconform to existing (or yet to be developed) standards, such as, forexample, cellular communications including LTE (Long Term Evolution),Wireless Fidelity (Wi-Fi), Bluetooth, and/or Near Field Communication(NFC). Exemplary wireless networks include, but are not limited to,wireless local area networks, wireless personal area networks, wirelessmetropolitan area networks, cellular networks, and satellite networks.

I/O system 860 may be configured to interface between various I/Odevices and other components of platform 800. I/O devices may include,but not be limited to, user interface 862 and display element 864. Userinterface 862 may include other devices (not shown) such as a touchpad,keyboard, mouse, microphone and speaker, trackball or scratch pad, andcamera. I/O system 860 may include a graphics subsystem configured toperform processing of images for rendering on the display element 864.These images may be provided by tomographic processing system 110.Graphics subsystem may be a graphics processing unit or a visualprocessing unit (VPU), for example. An analog or digital interface maybe used to communicatively couple graphics subsystem and the displayelement. For example, the interface may be any of a high definitionmultimedia interface (HDMI), DisplayPort, wireless HDMI, and/or anyother suitable interface using wireless high definition complianttechniques. In some embodiments, the graphics subsystem could beintegrated into processor 820 or any chipset of platform 800.

It will be appreciated that in some embodiments, some of the variouscomponents of platform 800 may be combined or integrated in asystem-on-a-chip (SoC) architecture. In some embodiments, the componentsmay be hardware components, firmware components, software components orany suitable combination of hardware, firmware or software.

Tomographic processing system 110 is configured to generate relativelyhigh resolution 3-dimensional images of the sample object 140, based onmeasured photon counts and energies, using the imaging system 100,employing a nanofabricated target structure, as described previously.Imaging system 100 may include any or all of the components illustratedin FIGS. 1-5 as described above. These components can be implemented orotherwise used in conjunction with a variety of suitable hardware thatis coupled to or that otherwise forms a part of platform 800. The targetnanostructures enable sub-beam resolution, but ultimate imagingresolution also depends on a number of factors including X-raysensitivity (contrast) to the materials in the sample under study,geometric diversity of X-ray sampling of the structure as defined, atleast, by (i) spatial distribution of beam probe locations with respectto the target/sample assembly, (ii) rotation angle(s) of thetarget/sample assembly with respect to the probe beam optical axis,(iii) number and spatial distribution of detector pixels used in thetransmission X-ray measurement, (iv) distance of detector pixels fromthe target/sample assembly, (v) absolute number of photon counts of theimaging X-rays (which determines data variance), (vi) detectedsignal-to-noise ratio, and (vii) the optimization procedure used in thetomographic inversion (including the selection of regularization ormodel priors).

Various embodiments of platform 800 may be implemented using hardwareelements, software elements, or a combination of both. Examples ofhardware elements may include processors, microprocessors, circuits,circuit elements (for example, transistors, resistors, capacitors,inductors, and so forth), integrated circuits, ASICs, programmable logicdevices, digital signal processors, FPGAs, logic gates, registers,semiconductor devices, chips, microchips, chipsets, and so forth.Examples of software may include software components, programs,applications, computer programs, application programs, system programs,machine programs, operating system software, middleware, firmware,software modules, routines, subroutines, functions, methods, procedures,software interfaces, application program interfaces, instruction sets,computing code, computer code, code segments, computer code segments,words, values, symbols, or any combination thereof. Determining whetheran embodiment is implemented using hardware elements and/or softwareelements may vary in accordance with any number of factors, such asdesired computational rate, power level, heat tolerances, processingcycle budget, input data rates, output data rates, memory resources,data bus speeds, and other design or performance constraints.

The various embodiments disclosed herein can be implemented in variousforms of hardware, software, firmware, and/or special purposeprocessors. For example, in one embodiment at least one non-transitorycomputer readable storage medium has instructions encoded thereon that,when executed by one or more processors, causes one or more of themethodologies disclosed herein (for example, tomographic imageprocessing of the detected spectral energy) to be implemented. Othercomponentry and functionality not reflected in the illustrations will beapparent in light of this disclosure, and it will be appreciated thatother embodiments are not limited to any particular hardware or softwareconfiguration. Thus, in other embodiments platform 800 may compriseadditional, fewer, or alternative subcomponents as compared to thoseincluded in the example embodiment of FIG. 8.

Some embodiments may be described using the expression “coupled” and“connected” along with their derivatives. These terms are not intendedas synonyms for each other. For example, some embodiments may bedescribed using the terms “connected” and/or “coupled” to indicate thattwo or more elements are in direct physical or electrical contact witheach other. The term “coupled,” however, may also mean that two or moreelements are not in direct contact with each other, but yet stillcooperate or interact with each other.

The aforementioned non-transitory computer readable medium may be anysuitable medium for storing digital information, such as a hard drive, aserver, a flash memory, and/or random access memory (RAM), or acombination of memories. In alternative embodiments, the componentsand/or modules disclosed herein can be implemented with hardware,including gate level logic such as a field-programmable gate array(FPGA), or alternatively, a purpose-built semiconductor such as anapplication-specific integrated circuit (ASIC). In some embodiments, thehardware may be modeled or developed using hardware descriptionlanguages such as, for example Verilog or VHDL. Still other embodimentsmay be implemented with a microcontroller having a number ofinput/output ports for receiving and outputting data, and a number ofembedded routines for carrying out the various functionalities disclosedherein. It will be apparent that any suitable combination of hardware,software, and firmware can be used, and that other embodiments are notlimited to any particular system architecture.

Some embodiments may be implemented, for example, using a machinereadable medium or article which may store an instruction or a set ofinstructions that, if executed by a machine, may cause the machine toperform a method and/or operations in accordance with the embodiments.Such a machine may include, for example, any suitable processingplatform, computing platform, computing device, processing device,computing system, processing system, computer, process, or the like, andmay be implemented using any suitable combination of hardware and/orsoftware. The machine readable medium or article may include, forexample, any suitable type of memory unit, memory device, memoryarticle, memory medium, storage device, storage article, storage medium,and/or storage unit, such as memory, removable or non-removable media,erasable or non-erasable media, writeable or rewriteable media, digitalor analog media, hard disk, floppy disk, compact disk read only memory(CD-ROM), compact disk recordable (CD-R) memory, compact diskrewriteable (CD-RW) memory, optical disk, magnetic media,magneto-optical media, removable memory cards or disks, various types ofdigital versatile disk (DVD), a tape, a cassette, or the like. Theinstructions may include any suitable type of code, such as source code,compiled code, interpreted code, executable code, static code, dynamiccode, encrypted code, and the like, implemented using any suitable highlevel, low level, object oriented, visual, compiled, and/or interpretedprogramming language.

Unless specifically stated otherwise, it may be appreciated that termssuch as “processing,” “computing,” “calculating,” “estimating,”“determining,” or the like refer to the action and/or process of acomputer or computing system, or similar electronic computing device,that manipulates and/or transforms data represented as physicalquantities (for example, electronic) within the registers and/or memoryunits of the computer system into other data similarly represented asphysical quantities within the registers, memory units, or other suchinformation storage transmission or displays of the computer system. Theembodiments are not limited in this context.

The terms “circuit” or “circuitry,” as used in any embodiment herein,are functional and may comprise, for example, singly or in anycombination, hardwired circuitry, programmable circuitry such ascomputer processors comprising one or more individual instructionprocessing cores, state machine circuitry, and/or firmware that storesinstructions executed by programmable circuitry. The circuitry mayinclude a processor and/or controller configured to execute one or moreinstructions to perform one or more operations described herein. Theinstructions may be embodied as, for example, an application, software,firmware, or one or more embedded routines configured to cause thecircuitry to perform any of the aforementioned operations. Software maybe embodied as a software package, code, instructions, instruction setsand/or data recorded on a computer-readable storage device. Software maybe embodied or implemented to include any number of processes, andprocesses, in turn, may be embodied or implemented to include any numberof threads or parallel processes in a hierarchical fashion. Firmware maybe embodied as code, instructions or instruction sets and/or data thatare hard-coded (e.g., nonvolatile) in memory devices. The circuitry may,collectively or individually, be embodied as circuitry that forms partof a larger system, for example, an integrated circuit (IC), anapplication-specific integrated circuit (ASIC), a system-on-a-chip(SoC), computers, and other processor-based or functional systems. Otherembodiments may be implemented as software executed by a programmablecontrol device. In such cases, the terms “circuit” or “circuitry” areintended to include a combination of software and hardware such as aprogrammable control device or a processor capable of executing thesoftware. As described herein, various embodiments may be implementedusing hardware elements, software elements, or any combination thereof.Examples of hardware elements may include processors, microprocessors,circuits, circuit elements (e.g., transistors, resistors, capacitors,inductors, and so forth), integrated circuits, application specificintegrated circuits (ASIC), programmable logic devices (PLD), digitalsignal processors (DSP), field programmable gate array (FPGA), logicgates, registers, semiconductor device, chips, microchips, chip sets,and so forth.

Numerous specific details have been set forth herein to provide athorough understanding of the embodiments. It will be understood by anordinarily-skilled artisan, however, that the embodiments may bepracticed without these specific details. In other instances, well knownoperations, components and circuits have not been described in detail soas not to obscure the embodiments. It can be appreciated that thespecific structural and functional details disclosed herein may berepresentative and do not necessarily limit the scope of theembodiments. In addition, although the subject matter has been describedin language specific to structural features and/or methodological acts,it is to be understood that the subject matter defined in the appendedclaims is not necessarily limited to the specific features or actsdescribed herein. Rather, the specific features and acts describedherein are disclosed as example forms of implementing the claims.

Further Example Embodiments

The following examples pertain to further embodiments, from whichnumerous permutations and configurations will be apparent.

One example embodiment of the present disclosure provides an imagingsystem comprising: a target structure comprising a first surface and asecond surface, the second surface opposite the first surface; one ormore materials disposed on the first surface of the target structure; aprimary particle beam source to provide a particle flux incident on anarea of the first surface of the target structure, the area encompassingone or more of the materials, such that the one or more materialsgenerate secondary X-rays of characteristic energies in response to theparticle flux, the characteristic energies based on properties of thematerials; and a spectral energy detector (SED) to detect and measurethe secondary X-rays, wherein the secondary X-rays are attenuated bypropagation through a sample to be imaged, the sample positioned bothadjacent to the second surface of the target structure and between thetarget structure and the SED.

In some cases, the particle flux comprises one of electrons, photons,and ions. In some cases, the area upon which the particle flux isincident is of a first diameter, focal spots of the secondary X-rays areof one or more additional diameters related to diameters of thematerials, and the first diameter is greater than the one or moreadditional diameters. In some such cases, the secondary X-rays providean imaging resolution related to the one or more additional diameters.In some such cases, the one or more additional diameters are less thanor equal to one micron. In some cases, the secondary X-rays propagateisotropically from the materials. In some cases, the materials includeat least one of hafnium, tantalum, tungsten, bismuth, gold, lead, zinc,copper, germanium, titanium, chromium, nickel, and platinum. In somecases, the characteristic energies are unique to the materials. In somecases, the materials are disposed on the first surface of the targetstructure in a hexagonal pattern. In some cases, the system furthercomprises a fixture to secure the target structure and the sample, andto rotate and/or translate the target structure and sample relative tothe primary particle beam source to provide tomographic imagingcapability.

Another example embodiment of the present disclosure provides a methodfor imaging, the method comprising: providing a primary particle beam toilluminate an area of a first surface of a target structure, the areaencompassing one or more materials disposed on the first surface of thetarget structure, such that the one or more materials generate secondaryX-rays in response to the primary particle beam; and detecting, by aspectral energy detector (SED), attenuation of the secondary X-rays,wherein the secondary X-rays are attenuated by passage through a sampleto be imaged, the sample positioned both adjacent to a second surface ofthe target structure and between the target structure and the SED. Insome cases, the primary particle beam comprises one of electrons,photons, and ions. In some cases, the primary particle beam is of afirst diameter, focal spots of the secondary X-rays are of one or moreadditional diameters related to diameters of the materials, and thefirst diameter is greater than the one or more additional diameters. Insome such cases, the secondary X-rays provide an imaging resolutionrelated to the one or more additional diameters. In some such cases, theone or more additional diameters are less than or equal to one micron.In some cases, the secondary X-rays propagate isotropically from thematerials. In some cases, the materials include at least one of hafnium,tantalum, tungsten, bismuth, gold, lead, zinc, copper, germanium,titanium, chromium, nickel, and platinum. In some cases, thecharacteristic energies are unique to the materials. In some cases, thematerials are disposed on the first surface of the target structure in ahexagonal pattern. In some cases, the system further comprises rotatingand/or translating the target structure and the sample, relative to asource of the primary particle beam, to provide tomographic imagingcapability.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention,in the use of such terms and expressions, of excluding any equivalentsof the features shown and described (or portions thereof), and it isrecognized that various modifications are possible within the scope ofthe claims. Accordingly, the claims are intended to cover all suchequivalents. Various features, aspects, and embodiments have beendescribed herein. The features, aspects, and embodiments are susceptibleto combination with one another as well as to variation andmodification, as will be understood by those having skill in the art.The present disclosure should, therefore, be considered to encompasssuch combinations, variations, and modifications. It is intended thatthe scope of the present disclosure be limited not by this detaileddescription, but rather by the claims appended hereto. Future filedapplications claiming priority to this application may claim thedisclosed subject matter in a different manner, and may generallyinclude any set of one or more elements as variously disclosed orotherwise demonstrated herein.

What is claimed is:
 1. An imaging system comprising: a target structurecomprising a first surface and a second surface, the second surfaceopposite the first surface; one or more materials disposed on the firstsurface of the target structure; a primary particle beam source toprovide a particle flux incident on an area of the first surface of thetarget structure, the area encompassing the one or more materials, suchthat the one or more materials generate secondary X-rays ofcharacteristic energies in response to the particle flux, thecharacteristic energies based on properties of the materials; and aspectral energy detector (SED) to detect and measure the secondaryX-rays, wherein the secondary X-rays are attenuated by propagationthrough a sample to be imaged, the sample positioned both adjacent tothe second surface of the target structure and between the targetstructure and the SED.
 2. The system of claim 1, wherein the particleflux comprises one of electrons, photons, and ions.
 3. The system ofclaim 1, wherein the area upon which the particle flux is incident is ofa first diameter, focal spots of the secondary X-rays are of one or moreadditional diameters related to diameters of the materials, and thefirst diameter is greater than the one or more additional diameters. 4.The system of claim 3, wherein the secondary X-rays provide an imagingresolution related to the one or more additional diameters.
 5. Thesystem of claim 3, wherein the one or more additional diameters are lessthan or equal to one micron.
 6. The system of claim 1, wherein thesecondary X-rays propagate isotropically from the materials.
 7. Thesystem of claim 1, wherein the materials include at least one ofhafnium, tantalum, tungsten, bismuth, gold, lead, zinc, copper,germanium, titanium, chromium, nickel, and platinum.
 8. The system ofclaim 1, wherein the characteristic energies are unique to thematerials.
 9. The system of claim 1, further comprising a plurality ofsensors on the spectral energy detector, wherein an image of the sampleis formed based on signals generated by the sensors detecting thesecondary X-rays.
 10. The system of claim 1, further comprising afixture to secure the target structure and the sample, and to rotateand/or translate the target structure and sample relative to the primaryparticle beam source to provide tomographic imaging capability.
 11. Amethod for imaging, the method comprising: providing a primary particlebeam to illuminate an area of a first surface of a target structure, thearea encompassing one or more materials disposed on the first surface ofthe target structure, such that the one or more materials generatesecondary X-rays in response to the primary particle beam; anddetecting, by a spectral energy detector (SED), attenuation of thesecondary X-rays, wherein the secondary X-rays are attenuated by passagethrough a sample to be imaged, the sample positioned both adjacent to asecond surface of the target structure and between the target structureand the SED.
 12. The method of claim 11, wherein the primary particlebeam comprises one of electrons, photons, and ions.
 13. The method ofclaim 11, wherein the primary particle beam is of a first diameter,focal spots of the secondary X-rays are of one or more additionaldiameters related to diameters of the materials, and the first diameteris greater than the one or more additional diameters.
 14. The method ofclaim 13, wherein the secondary X-rays provide an imaging resolutionrelated to the one or more additional diameters.
 15. The method of claim13, wherein the one or more additional diameters are less than or equalto one micron.
 16. The method of claim 11, wherein the secondary X-rayspropagate isotropically from the materials.
 17. The method of claim 11,wherein the materials include at least one of hafnium, tantalum,tungsten, bismuth, gold, lead, zinc, copper, germanium, titanium,chromium, nickel, and platinum.
 18. The method of claim 11, wherein thecharacteristic energies are unique to the materials.
 19. The method ofclaim 11, wherein the materials are disposed on the first surface of thetarget structure in a hexagonal pattern.
 20. The method of claim 11,further comprising rotating and/or translating the target structure andthe sample, relative to a source of the primary particle beam, toprovide tomographic imaging capability.